Why do we have long fingerprints?

BEIJING, Dec. 26 (Xinhua) — A man named Thomas Jennings fled the scene in 1910 after the killing, but left a complete fingerprint on the railing outside the crime scene, leading to his conviction in 1911, according tomedia reports. This is the first time fingerprints have been used as evidence in criminal investigations.

Why do we have long fingerprints?

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Fingerprints have since been seen as a key piece of evidence in criminal investigations. Since everyone’s fingerprints are unique, fingerprints are undoubtedly a great tool to solve cases, almost as if they were born for this purpose.

But of course that is not the case. So here’s the question: Why do we have fingerprints? What exactly is the biological significance of fingerprints?

Fingers and friction

In fact, scientists have been arguing over the answer to this question.

According to Roland Ennos, a biomechanics researcher and visiting professor of biology at the University of Hull in the UK, there are two views on fingerprints: that they help enhance friction when grip is held, and that it helps enhance touch.

Ennos has studied the first idea that fingerprints enhance our grip. For a long time, the theory has been dominant that the tiny grooves of fingerprints can create friction between the hand and the surface of the object.

Fingerprints may work in a way similar to a car’s rubber tire. Rubber is naturally flexible and fits well on the ground. In addition, the pattern of grooves on the tires increases the surface area of the tire, further enhancing its friction and grip. This may support the idea that fingerprints can enhance the friction of the fingertips. To this end, Ennos conducted validation in the laboratory.

“We wanted to see if the fingerprints could be like a tire pattern, enhancing the friction between the fingertips and the exposed surface. To find out, the researchers placed an plexiglass plate between the fingertips of the subjects’ hands, applied them a force of different sizes, and used the mud to determine the area of contact between the fingertips and the glass.

The results were quite surprising: because the grooves of the fingerprints could not touch the glass, the fingerprints reduced the area of contact between the fingertips and the glass. In other words, fingerprints appear to reduce friction compared to smooth skin in the rest of the body, at least on smooth surfaces.

But Ennos points out that this does not completely overturn the theory that “fingerprints enhance grip”. Perhaps fingerprints can increase the friction between the fingertips and the surface of the object in wet conditions, just as the pattern of a tire can be drained by a capillary. But this view is more difficult to verify because it is difficult to accurately simulate the performance of human fingerprints under these conditions.

But don’t forget, there’s another point of view.

Subtle touch

A few years ago, a biologist at the University of Paris, Georges Debregeas, suddenly became interested in the role of touch when he pondered why humans had fingerprints. Our fingertips are distributed with four mechanical receptors, cells that react to mechanical stimuli such as touch. Debregias is particularly interested in one of the receptors, called the Pacinian corpuscles. The receptor is located approximately 2 mm below the skin of the fingertip. “The reason I’m interested in it is that we’ve learned from previous experiments that these receptors can regulate the perception of fine textures. “

These mechanical receptors are particularly sensitive to weak vibrations with a frequency of 200 Hz, thus giving the fingertips a very high sensitivity. Debregias wanted to know if fingerprints reinforced this sensitivity.

To find out, he and his colleagues designed a bionic tactile sensor that mimics the structure of a human finger and is equipped with a Pasini-like small body that detects faint vibrations. They made two versions, one with a smooth surface and the other with a trench-like structure similar to a human fingerprint. The researchers were surprised to see that the trench structure on the second device could amplify the vibration of a particular frequency, and that the Pasini-style small body was the most sensitive to the vibration of that frequency.

This suggests that human fingerprints may also screen for vibrations at specific frequencies and pass the filtered vibrations to the mechanical receptors beneath the skin. The theory is that by amplifying this fine sensory information, fingerprints can enhance our tactile sensitivity. As Debregias puts it: “The fingerprints on the skin have completely changed the nature of these tactile signals.” “

But what good is this super-sensitive fingertip?

For thousands of years, our hands have been a key tool for helping us forage, eat, and explore the world, tasks that need to be accomplished with touch. From an evolutionary point of view, sensitivity to texture sits especially important because it helps us find the right food, distinguish it from the food that can be imported from the food in question, and prevent us from eating something that is corrupt and spoiled.

Debregias also noted that such fingerprints are also “paired” with Pasini-style small bodies in animals such as chimpanzees and koalas that require sensitive tactile foraging.

But he also stressed that the experiments do not prove that fingerprints evolved for these purposes. But this theory is persuasive, as if “everything is right”.

No conclusion

In fact, Debregias believes that humans may have evolved fingerprints for both purposes. “We’re so good at manipulating and grasping objects because we have a great sense of touch that creates an continuous feedback loop between what we touch and how we feel, helping us adjust the force of our fingers applied to the object in real time. “

For example, if something you hold in your hand is about to slip, you need to feel the change on the surface of an object with a sensitive fingertip to hold it firmly. So Debregias believes that our fine touch and precision grip ability are actually complementary and co-evolutionary.

Ennos also offers another possible explanation: fingerprints may prevent long blisters at the fingertips. The trench-like structure of the fingerprint may in some directions strengthen the skin and inhibit blister spawning, while also allowing the skin to stretch at a specific angle and maintain contact with the surface of the object, somewhat similar to the steel cords used to reinforce tires.

So what’s the final conclusion? For the time being, apart from providing the police with evidence of a cructoed crime, the purpose of fingerprinting remains an open mystery to us.

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